Spin-Hall effect
Encyclopedia
The Spin Hall Effect is a transport phenomenon predicted by Russian physicists M.I. Dyakonov and V.I. Perel in 1971. It consists of the appearance of spin
accumulation on the lateral surfaces of a current-carrying sample, the signs of the spin directions being opposite on the opposing boundaries. In a cylindrical wire, the current-induced surface spins will wind around the wire. When the current direction is reversed, the directions of spin orientation is also reversed.
The term "Spin Hall Effect" was introduced by Hirsch in 1999. Indeed, it is somewhat similar to the classical
Hall effect
, where charges of opposite sign appear on the opposing lateral surfaces to compensate for the
Lorentz force
, acting on electrons in an applied magnetic field. However, no magnetic field is needed for SHE. On the contrary, if a strong enough magnetic field is applied in the direction perpendicular to the orientation of the spins at the surfaces, SHE will disappear because of the spin precession around the direction of the magnetic field.
Experimentally, the Spin Hall Effect was observed in semiconductors more than 30 years after the original prediction. The spin accumulation induces circular polarization of the emitted light, as well as the Faraday (or Kerr) polarization rotation of the transmitted (or reflected) light, which allows to monitor SHE by optical means.
The origin of SHE is in the spin-orbit interaction
, which leads to the coupling of spin and charge currents: an electrical current induces a transverse spin current (a flow of spins) and vice versa. One can intuitively understand this effect by using the analogy between an electron and a spinning tennis ball, which deviates from its straight path in air in a direction depending on the sense of rotation (the Magnus effect
).
The Inverse Spin Hall Effect, an electrical current induced by a spin flow due to a space dependent spin polarization, was first observed in 1984. More recently, the existence of both direct and inverse effects was demonstrated not only in semiconductors, but also in metals.
The SHE belongs to the same family as the anomalous Hall effect, known for a long time in ferromagnets, which also originates from spin-orbit interaction.
The SHE might be used to manipulate electron spins electrically. For example, in combination with the electric stirring effect, the SHE leads to spin polarization in a localized conducting region.
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...
accumulation on the lateral surfaces of a current-carrying sample, the signs of the spin directions being opposite on the opposing boundaries. In a cylindrical wire, the current-induced surface spins will wind around the wire. When the current direction is reversed, the directions of spin orientation is also reversed.
The term "Spin Hall Effect" was introduced by Hirsch in 1999. Indeed, it is somewhat similar to the classical
Hall effect
Hall effect
The Hall effect is the production of a voltage difference across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current...
, where charges of opposite sign appear on the opposing lateral surfaces to compensate for the
Lorentz force
Lorentz force
In physics, the Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields:...
, acting on electrons in an applied magnetic field. However, no magnetic field is needed for SHE. On the contrary, if a strong enough magnetic field is applied in the direction perpendicular to the orientation of the spins at the surfaces, SHE will disappear because of the spin precession around the direction of the magnetic field.
Experimentally, the Spin Hall Effect was observed in semiconductors more than 30 years after the original prediction. The spin accumulation induces circular polarization of the emitted light, as well as the Faraday (or Kerr) polarization rotation of the transmitted (or reflected) light, which allows to monitor SHE by optical means.
The origin of SHE is in the spin-orbit interaction
Spin-orbit interaction
In quantum physics, the spin-orbit interaction is any interaction of a particle's spin with its motion. The first and best known example of this is that spin-orbit interaction causes shifts in an electron's atomic energy levels due to electromagnetic interaction between the electron's spin and...
, which leads to the coupling of spin and charge currents: an electrical current induces a transverse spin current (a flow of spins) and vice versa. One can intuitively understand this effect by using the analogy between an electron and a spinning tennis ball, which deviates from its straight path in air in a direction depending on the sense of rotation (the Magnus effect
Magnus effect
The Magnus effect is the phenomenon whereby a spinning object flying in a fluid creates a whirlpool of fluid around itself, and experiences a force perpendicular to the line of motion...
).
The Inverse Spin Hall Effect, an electrical current induced by a spin flow due to a space dependent spin polarization, was first observed in 1984. More recently, the existence of both direct and inverse effects was demonstrated not only in semiconductors, but also in metals.
The SHE belongs to the same family as the anomalous Hall effect, known for a long time in ferromagnets, which also originates from spin-orbit interaction.
The SHE might be used to manipulate electron spins electrically. For example, in combination with the electric stirring effect, the SHE leads to spin polarization in a localized conducting region.